This invention is directed to transfer ports for movement of materials from one clean room to another, and is more particularly directed to a port assembly in which contaminated areas of respective port surfaces are sealed off from contact with the interior of the clean rooms to minimize the amount of particulate matter introduced into the clean room when the port assembly is opened. The invention is specifically intended for a transfer port which permits movement of clean material between Class 1 clean rooms with no change in contamination levels.
High density circuit integration requires an extremely high standard in contamination control. This is especially true in the manufacture of semiconductor sub-micron geometry integrated circuits. The semi-conductor industry has developed the ability to create thousands of circuits upon a miniature chip, but the ability to practice this efficiently is possible only where substantially all sub-micron contaminants particles are eliminated from the air that contacts the semiconductor wafers. Other manufacturing industries, such as thin-film processing, opto-electronics, powder metallurgy, paints, pigments, and those employing critical assemblies such as laser and hard disk drives, have improved their production yields by careful control of particulate contaminants.
Industries that require contamination control to protect the users of their products include pharmaceutical manufacturers, food processors, manufacturers of medical devices e.g. surgical needles and artificial joints. In health care, environmental control can be critical to surgical procedures and special patient care, especially in delicate cases such as immune deficiency or severe burns.
To benefit any of the above-mentioned industries and practices, it is envisioned that a suitable clean room environment would include a number of interlinked clean rooms, which would be small and modular in order to achieve Class 1 conditions. In such a system, small, modular clean rooms would serve as micro-environments or work cells which would be integrated into the manufacturing process with robots and automated material handling equipment. In this system, the material handling equipment would consist of internally clean containers, or xe2x80x9cclean boxes,xe2x80x9d arranged as automatic transporters, where the clean boxes would carry material between the clean micro-environments in the various work cells. This concept is advantageous in that most of the contaminants and particle-shedding moving parts are external to the clean environment, so that contaminants inside the clean environment would be much easier to control. Also, in such a system, the area in which human workers are present would be outside the clean environment. This means that the workers are free to move about without gowns or other awkward clothing because they are removed from the clean space. Also, because temperature and humidity control are required for maintenance of the clean work space, the modular microenvironment concept represents a major energy savings, because the workers are no longer contributing to the humidity and temperature in the clean space.
However, a key to this modular system is the ability to move work material between modular clean rooms and transport containers without contamination of the material or the clean space. This requires that the clean rooms and the clean transport containers be provided with a port or door system that limits the amount of contamination from the port when opened to connect the clean box to the clean room, but which can be left exposed to the exterior environment when the clean box is traveling between stations. Because the exterior surfaces of the clean box transporters and the clean room work cells are exposed to contamination, this requires that the contamination between these surfaces be isolated to as small a volume as possible. The object is to provide a doorway through which the clean material can pass uncontaminated between the clean box and clean room.
Modular clean rooms are currently available, e.g., as described in U.S. Pat. No. 4,667,580, which can serve as clean microenvironment work cells. A tracked, automated transport system, employing electrically powered cars capable of being adapted to clean box transports, is also available e.g. as described in U.S. Pat. Nos. 3,340,821 and 4,630,216. However, these presently-available items lack a port arrangement through which the workpiece material can pass uncontaminated.
One approach to transporting of materials between clean environments has been the standardized mechanical interface, or SMIF, e.g., as described in U.S. Pat. Nos. 4,534,389 and 4,532,970. In the SMIF system a small box is provided to carry semiconductor wafers or the like from one machine to another machine. The SMIF system joins the machines to the boxes by a pair of dockable doors. These doors fit together to trap contaminant particles that are on the outer surfaces of the doors. Once linked together, the doors move a s a unit into the clean interior space of the machine. However, the SMIF system has no structure to control or limit contamination at the split lines, i.e., where the doors close onto their respective chambers. The amount of contamination from this area can be considerable when Class 1 conditions are observed.
In this discussion of clean environments, the xe2x80x9cclassxe2x80x9d of the environment indicates the maximum possible number of particles 0.5 microns in diameter or larger in each one cubic foot of air. Thus, a xe2x80x9cClass 1xe2x80x9d environment contains one such particle for each cubic foot of air, a xe2x80x9cClass 10xe2x80x9d environment may have ten times as many particles for each unit volume.
It is an object of this invention to provide a system for movement of material, without contamination, between Class 1 clean room module work stations.
It is another object of this invention to provide a mating port system for the modular clean room and clean box transporter which permit transfer between the clean room and clean box without contamination of the material.
It is a further object of this invention to provide a transfer port assembly in which the surfaces of the clean room and clean box ports, that are exposed to the contaminated environment and are exposed to the clean environment during transfer, are confined to a limited volume which can be substantially cleaned of particulate contaminants prior to opening the ports.
In accordance with an aspect of this invention, an interengaging port assembly mates a clean box type transporter to a modular clean room to permit transfer of materials between the clean box transporter and the clean room without contaminating the interiors of the clean room and clean box, and without contaminating the material. A port assembly portion on the clean box transporter includes a door that has an outer surface exposed to the contaminated environment and an inner surface that faces the interior of the clean box. The clean box port also includes a flat wall portion of the box which has an opening therein that accommodates the door, the opening having a peripheral recess surrounding a central passage so that a transverse surface of the peripheral recess mates against a peripheral surface of the door, with a seal, e.g., a sealing ring disposed between these transverse surfaces. This seals the interior of the clean room from an annular split space that is defined between the opening and the periphery of the door. A clean room port is disposed on each of the clean room modules, and includes a clean room door that has an outer surface of the same dimensions as the outer surface of the clean box door. The clean room door also has a transverse peripheral flange entirely surrounding the door on the side away from its outer surface. An opening in one flat wall of the clean room accommodates the clean room port door and is dimensioned so that the clean room port door can be retracted into the interior. The clean box door, which is held onto the clean room door, passes with it through the clean room port opening. There is a first seal on the outer surface of the clean room wall outside the rim of the opening and entirely surrounding it to seal between the clean room wall and the wall of the clean box outside the rim of the clean box opening. A second seal is disposed on the clean room door and is disposed a short distance in from the rim of the door. This seals against the clean box door and seals off substantially all of the contaminated outer surfaces thereof from the split space that was referred to earlier. A third seal is disposed on the transverse flange of the clean room port door to seal the interior of the clean room module from an annular split volume that is defined by the opening in the clean room wall and the periphery of the clean room prot door. The seal of the clean box port together with the first, second, and third seals define a limited volume that is exposed to the contaminated ambient when the clean box and clean room are remote from one another, and is also in communication with the interiors of the clean room and clean box when the port is opened.
When the materials are to be transferred from a clean box to the clean room or vice versa, the clean box transporter is brought into position alongside the clean room and the clean box port is brought into registry with the clean room port. Then the doors are clamped together, e.g. by applying vacuum to the contaminated space defined within the second seal. The clean box is also held firmly against the clean room wall. To this end, a fourth seal can be disposed on the outer surface of the clean room wall outside the first seal to define an annular volume between the first and fourth seals and between the facing flat surfaces of the clean room and clean box. A vacuum applied to this volume clamps the clean box in position and also ensures a good seal around the openings of the clean room port and clean box port. The limited volume at the split between the doors and their respective openings is flushed with a clean gas and/or a vacuum is applied to remove as much of the particulate matter as possible from the surfaces there. Then the door is slowly opened towards the interior of the clean room. There is a slightly higher pressure in the clean box than in the clean room, so that when the port assembly is opened, there will be an air flow into the clean room. This flow carriers any particulates in and away from the materials in the clean box. The small number of particles resulting from this become entrained in the clean room air flow and are filtered out. After this, the material transfer takes place without contamination, and then the opening process is reversed to close the port doors. A latch mechanism in the clean box port door holds the door closed and sealed in place in the clean box opening.
The clean box transporter is preferably a miniature clean room in that it recirculates and filters air to maintain a clean environment within. The clean box contains an air handling mechanism, preferably producing a gentle, laminar air flow within the box, while filtering the recirculating air through a high efficiency particulate air (HEPA) filter system. The clean box can be of a design with self-propelled drive and wheels which follow a track to the various clean room module work stations.